Pyrazine bridged dicobaloximes with bis(thiophenyl)glyoxime and their molecular oxygen insertion

Abstract

The pyrazine bridged dicobaloxime complexes [RCo(dSPhgH)2]2-μ-Pz [R = Et, Bu, CH2Ph] (1–3) with bis(thiophenyl)glyoxime, (dSPhgH2) have been synthesized and characterized by NMR spectroscopy for the first time. The X-ray structures of 2 and 3 are also reported. A cyclic voltammetry study shows the two cobalt centers are reduced and oxidized at different potentials as two discrete units. Molecular oxygen insertion into the Co–C bond in the complexes 1 and 3 under photochemical conditions leads to formation of [RCH2(O2)Co(dSPhgH)2]2-μ-Pz [R = CH3, Ph]. Careful monitoring of the reaction by 1H NMR reveals formation of a mixture of products RCH2(O2)Co(dSPhgH)2-Pz-Co(dSPhgH)2CH2R and [RCH2(O2)Co(dSPhgH)2]2-μ-Pz [R = CH3, Ph] at the initial stage of the reaction corresponding to mono and bis insertion. The ratio of these products changes with time and finally [RCH2(O2)Co(dSPhgH)2]2-μ-Pz [R = CH3, Ph] was isolated as the only product. Molecular oxygen insertion reaction in [PhCH2Co(dmgH)2]2-μ-Pz has also been monitored for comparison purpose.